Rotary hammer mill



Spt. 5, 1939. T. c. ALFRED 2,172,096

ROTARY HAMMER MILL Original Filed Sept. 11, 1933 3 Sheets-Sheet l a 3 T(7p 20 A .34 6

I 364 I 0 4; I o 4/ Q 2 \J] 44 Z? 0 0 o 6 J 1 I wodoitC-ldfired' Sept.5, 1939 T. c. ALFRED. 2,172,096

- ROTARY HAMMER MILL I Original Filed Sept. 11, 1933 I 3 Sheet s Sheet 2Sept. 5,1939. T LFR D 7 2,172,096

' ROTARY HAMMERMILL Original Filed Sept. 11, 1933 :5 sne' ts sheet s IPatented gept. 5, 1939 IPATENT- OFFICE ROTARY HAMMER. MILL Theodore 0.Alfred, Lancaster, Ohio Application September 11, 1933, Serial No.688,970 Renewed May 15, 1937 1 Claim.

This invention relates to improvements. in rotary hammer mills of thecharacter employed in grinding or reducing various products such asgrain, stocks, seed, minerals and the like to a desired state ofsubdivision, the primary object of the invention being to provide agenerally improved and more eflicient machine for work of this characterand one wherein high grinding capacity is provided with relatively lowpower consumption.

With these and other objects in view, which will appear as thedescription proceeds, the invention consists in the novel features ofconstruction, combination of elements and arrangements of partshereinafter fully described and pointed out in the appended claim.

In the accompanying drawings:

Fig.' 1 is a side elevation .of a rotary hammer mill formed inaccordance with the present invention; a Fig. 2 is a front elevationthereof;

Fig. 3 is a vertical longitudinal sectional view taken through the mill;

Fig. 4 is a horizontal transverse sectional view on the line 4-4 of Fig.3;

Fig. 5 is a perspective view of the mill with the casing plates at oneside removed to disclose its interior structure;

Fig. 6 is a vertical transverse sectional view taken through the rotor;

Fig. 7 is a. detailed view of the cam operated fastening means forretaining the cover of the mill casing in secured engagement with thestationary lower section of the casing;

8 is a fragmentary sectional view of the rotor on the line 8--8 of Fig.6;

Fig. 9 is a detail sectional view taken on the line 99 of Fig. 1.

Referring more particularly to the drawings, the numeral I designatesthe casing of the reducing mill. Preferably, this casing comprises astationary lower section. A and a removable cover or hood section Bmounted on top of the lower section A when the mill is in operation.This casing may be constructed in any suitable manner from desiredmaterials. In the present form of the invention, however, the lowersection A comprises .vertically disposed corner angles I, horizontallyextending pairs of top and bottom angles 2 and transversely extendingtop angles 3. These angles are suitably bolted or otherwise secured in,rigid frame formation and also attached thereto are side and end plates4 and 5 respectively. The casing may be mounted 'upon any suitablefoundation either permanently or removably-in orderthat during operationof the mill a stable working base, free from objectionable vibration,may be provided.

The cover or hood section B also provides corner angles 6 to which issecured in any suitable 5 rigid manner a top plate I, side plates 8, anda vertical end plate 9, the latter being provided, contiguous to itslower edge, with a transversely and horizontally extending exteriorlydisposed angle member ID arranged above and in registra- 10 tion withthe top angle 3 of the base section A. The other side of the cover orhood B, opposed to the end plate 9, is substantially open, and carriesan inclined feed trough ll through or along which themateiials to bereduced are fed into the rotor chamber C of the casing-and below thedischarge end of the trough H, the hood section carries a transverselyand horizontally extending trap boxing I2 having the wall thereof whichcommunicates with the chamber C slotted as at IS in order totrap'undesirable solids, such as miscellaneous pieces of metal, andprevent their coming into contact with the grinding elements of themill. Preferably, studs l4 project from the ends of the boxing l2 andserve as fulcrums about which the hood section may turn in order to openor close the rotor chamber. Connected with the top wall 1 of the hoodsection is a slightly downwardly inclined baffle 15 which actsas adeflector in confining the material undergoing reduction to the limitsof the chamber C.

An important feature of the present invention resides in theconstruction of the rotor D. This rotor comprises, in the preferred formof the invention, an axial support in the form of a shaft I6 which issuitably journaled for rotation in connection with bearings I! mountedupon the upper surfaces of the top angles 2 of the base or lower sectionA. One end of this shaft carries a suitable form of belt wheel l8 bymeans of which power, obtained from any suitable form of prime mover,may be applied to the mill, whilethe opposite end of the shaft isconnected with a suctional fan 20, the latter being disposed in a casing2| arranged exteriorly and to one side of the mill casing, as shown moreparticularly in Fig. 2. The shaft I6, between the bearings i1, isthreaded as at 22 for the reception of clamping nuts 23, which functionto retain in assembled and clamped order a plurality of spaced flatbars, comprising secondary hammers and designated generally by thenumeral 24, in rotatable connection in unison with the shaft I 6. Ifdesired, the rotor shaft between its threaded portions 22 may be ofpolygonal design in tr'a'n sveisiegcros s 5? section for receptionwithin similarly formed openings provided in the intermediate portionsof the bars 26 which comprise the secondary hammers.

It will be observed that these secondary hammers comprise a multiplictyof flat substantially rectangular bars of uniform length which havetheir intermediate portions connected for unitary rotation with theshaft or other form of axial support I6. Further, these bars aredisposedin sets extending radially from the shaft l6 and are spacedsubstantially equidistantly at their outer ends to provide a pluralityof relatively -V-shaped pockets 25 therebetween, which pockets open tothe periphery of the rotor as shown in Fig. 3. These bars may be of anysuitable length and-are compactly secured together in side by siderelationship on the shaft for rotary movement in unison with the shaft,with the different sets of bars spaced equidistantly around the orbit oftravel of the rotor, and the advantages of this construction over theusual disc type of mounting, commonly found in grinding mills of thischaracter, will be more fully described herein after.

Each set of bars at' positions spaced from the axis l6 has theindividual bars thereof provided with registering perforations for thereception of transversely extending cross pins 26 which may be retainedin connection with the bars by having their outer ends equipped withcotter keys 21.

-The pins 26 are employed to provide pivotal mountings for the receptionof primary hammers 28.- Each of these hammers comprises a metalliccasting or stamping of a thickness to be freely received within thespaces provided between adjoining bars of a set, and the opposite endsof these primary hammers are formed with perforations 29 for thereception of the cross pins 26 by means of which the said primaryhammers are pivotally connected for independent swinging movement to theouter portions of the secondary hammers, so that while the primaryhammers revolve with the secondary hammers and the axial support l6, yetthey are permitted to respond freely to centrifugal forces, set up bythe rapid rotation of the rotor, usually a speed of 3300 R. P. M., toassume extended grinding positions wherein the outer ends of the primaryhammers project beyond the corresponding squared ends of the secondaryhammers. These primary hammers may be of the type disclosed in my priorPatent No. 9,325, which have here been selected for illustration andinclude somewhat tapering, stepped or shouldered ends 30, which havebeen found to be very effective in grinding operations of thischaracter. Following a certain amount of use of the primary hammers withresulting wear, the positions thereof in connection with the secondaryhammers or bars 24 may be reversed-to restore their normal operatingefficiency.

One of the serious disadvantages in the ordinary reducing mill asheretofore constructed has been the lack of proper rotor weights, whichhave been seriouslylacking in adequate fly wheel action. As aconsequence, rotors of prior design with which I have exeprimented arenot considered to possessa desired state of efficiency for the reasonthat they require an excessive amount of power for a given output ofground material. In the design of the present rotor, however, I havediscovered that by employing the grouped bars arranged in the compactfashion disclosed, the weight of the rotor may be increased to augmentthis fly wheel action and secure smoothness, lack of vibration, lowpower consumption and into the emciency of the mill, as a much harderblow is struck on the material being reduced than when a rotor ofsmaller diameter is used and, moreover, there is no loss in the actualnumber of blows struck per minute. This is a marked contrast with theusual type of rotor employing spacing discs for the centrifugal hammers.Such discs do not in the ordinary mill function to strike blows upon thematerial being reduced, as do the secondary hammers or bars, heredisclosed. In the present rotor, with the power input remainingconstant, the arms or bars provide increased diameter 'over the ordinarydisc type rotor, adequate weight for the desired fly wheel action,grinding or reducing operation from the bars or secondary hammers, andaugmented peripheral velocityof the outer or primary hammers carriedthereby.

In common with prior hammer mills of this general character, I employ asemicircular perforated plate or screen 3| beneath the lower half of therotor. In contrast, however, with previous screens, the screen 3| is setso that it is disposed slightlyeccentrically of the axis .of the rotor,or conversely the axis of the rotor is eccentric to that of the screen.This eccentricity issuch that the screen is spaced roughly atapproximately of an inch from the outer orbit of the rotor at the frontof the mill, tapering to approximately of an inch at the botom and toabout A; of an inch at the rear. These figures are of course approximateand are subject to variation if found desirable. By this eccentricity ofthe rotor with respect to the screen, I have been able to secure a moreeflicient grinding or reducing operation and have increased materiallythe capacity of the mill over the usual construction wherein the screenexactly conforms to the orbit of the rotor. In the operation of a screenof this character. it is important that it should shed finely dividedmaterials through the openings or perforations thereof rapidly so thatthe ground materials may pass freely therethrough. To this end I mountthe screen 3| in arcuate guides 32 in which the screen is free to moveuntil one end thereof con-' tacts with a stationary abutment 33 disposedadjacent to the trap l2. The opposite edge of the screen is then sodisposed as to engage with the lower portion of the cover or hoodB whenthe latter is closed, so that upon the final clamping of the hood in itsclosed position, the screen will be placed under compression, thepurpose of this being to maintain the screen in what may be termed atuned state when the mill is in operation so that the minute and rapidvibration thereof will serve to cause a rapid and effective passage ofthe finely ground materials through the perforations thereof.

To obtain thelocking of the hood in its closed position and the screenunder compression as described; the angle 3 of the base section isformed intermediately of its length with an opening for the reception ofa swinging eye bolt 34. This eye bolt, as shown in Fig. 7, is receivablewithin an open ended slot provided in the angle member In of the hoodsection. Also formed with the bolt 34 is a stationary cam enlargement36, which cooperates with a movable cam 31 which is turnable about theaxis of the bolt shank. The outer or upper end of the bolt maybeprovided with a nut 38 and a spring may be positioned between the nut 38and the movable cam 31. The cam is'provided with a lateral handleextension 40, and also a stop lug 4i. When this fastening is positionedin hood securing relationship, the handle 40 is actuated to rotate themovable cam until the stop lug 4| contacts with the end plate 9. Due tothe inclined plane action downward pressure will then be imparted to thehood causing it to exert a considerable force on one of the upperhorizontal edges of the screen to maintain the latter under compressionand at the same time to securely retain the hood section in closedoperative relationship with the stationary lower section of the millcasing.

The ground material drops into a trough 42 formed withinthe confines ofthe base section of the mill and is discharged therefrom by way of aconduit 43 by the suction created through the operation of the fan orblower 20. The divided material may then be delivered from the fan to asuitable form of separator (not shown) or other position of materialdeposit.

As set forth in my prior Patent No. 1,829,325, I

' there is a decided tendency for ground material to clog the openingsprovided in the upper portion of the screen at the front of the mill.Due to the curvature of the screen, the openings which extendtherethrough at this portion thereof are substantially horizontal, ormore nearly the horizontal than the vertical and, therefore, materialwhich collects in these openings does not so readily respond to gravityand as a'consequence the screen clogs in this area. To take care of thiscondition, the front of the mill in the present invention is providedwith a slot-open to the atmosphere and formed between the adjoiningedges of the laterally offset walls of one of the end plates 5 and thevertical'end plate 9, and through which slot air from the atmosphere maybe drawn. By the operation of the mill and the suction developed by theoperation of the fan 20, air drawn into the mill through the slot 44travels at a high velocity past the forward upper edge area of thescreen, creating suction forces by which materials which normally clogthat particular part of the screen arepositively removed fromobstructing positions and delivered to the trough 42 for subsequentdischarge from the mill.

Attention is directed to the cross sectional configuration of the hoodsection as more particularly disclosed in Fig. 3. The angles of the topplate I, the vertical end plate 9 and the deflector plate l5 are suchthat th'ematerial in this portion of the rotor chamber is kept movingback and forth on the rotor between the ends of the hammers and theangular walls of the hood, For example, theoretically, material fallingon a set of hammers when the latter are in a horizontal position, willbe thrown against the deflector bafiie I5 in the hood above the feedtable. While this material will not lose all of its rotary and forwardmotion, nevertheless, it will be deflected back onto ,the hammers tothen strike the slanting top wall 1 of the hood, thence again back uponthe hammers and into contact with the forward wall 9, being constantlyreduced by this agitation and contact with stationary or movingsurfaces, so that the material will be divided to a desired state by thetime it reaches the screen area. Preferably, the inner surfaces of thewalls I and 9 are provided with a screen lining as indicated at 45. Thislining not only changes the direction of the material contact therewithfrom a deflecting standpoint but it also has a certain cutting eifect onthe material at the edges of its openings, and, in addition, the liningserves to slow up or retard the forward motion of the feed or'othermaterial undergoing reduction.

It will be observed that the feed chute or trough H enters the rotorchamber at a point just.above the plane of the axial center of therotor. This is a considerably lower point than has been custom-\ ary inprevious hammer mill designs, and a dc?- clded advantage is obtained bythis lowering of the feed chute, in that it provides for a more extendedcontact between the primary and secondary hammers in the upper portion,of the rotor chamber, or in the hood area, with consequent greaterreduction of the material before the screen area is reached. It is inthis portion of the rotor chamber that the arms or .secondary hammersfunction as reducing agents since the large material readily drops intothe V-shaped spaces formed between the adjoining sets of bars or armscomprising the secondary hammers, but this is accomplished with but anegligible consumption of power. Where power is largely expended is inpassing the primary hammers through the bed of finely ground materialretained on the upper surfaces of the screen, but

since this bed rarely exceeds a depth in excess,

of of an inch, it will be seen that the secondary hammers or bars duringtheir travel through the lower half of the rotor chamber will be out ofcontact with the material being acted upon and thence will not consumeany appreciable power in this portion of the mill operation.

Any desired grouping of the primary hammers on the several sets of barsmay be provided. It is important however that the primary hammers shouldbe placed in such sequence between said bars that the rotor will besubstantially statically and dynamically balanced. Preferably, each setof bars carries eight hammers, four at each end,

as shown in Fig. 4.' By laterally offsetting the cation with the rotorchamber C so that as the' rotor revolves, any foreign particles, such asbits of metal or the like will, by centrifugal force, be advanced intothe boxing where such foreign particles will be imbedded in the reducedmate rial which collects in this boxing during the operation of themill. Preferably, the boxing is provided with a removable rear wall 41,which may be instantly removed by the mere loosening of the wing nut 48shown in Fig. 4, so that in the event of fire in the boxing, the'samemay be readily extinguished by the removal of the rear wall 41. Thelatter is ordinarily used for removing accumulated'particles of matterfrom the boxing.

The eccentricity of the screen mounting is such that in one of thecommercial forms of my improved hammer mill, the clearance between theends of the hammer and the screen proper at the forward upper end of thescreen is approximately three-fourths of an inch. This eccentricityprovides a clearance of approximately onehalf of an inch at the bottomof the screen and approximately one-fourth of an inch at the upper rearend of the screen. While this degree of eccentricity may be varied, theeccentricity thus afforded provides more freedom between the ends of thehammers and the screen in the threequarter inch space and allows,further reduction without as much drag or power consumption. In otherwords, the tapered circle admits larger portions at one end than would aconcentric circle only one-half an inch away from the ends of thehammers, doing away with shock loss at the point of entry over thescreen because of the greater space provided. At the other end, thereverse is true. However, by this time the materials are finely dividedand by operating the hammers closer to the screen, a greater output isobtained.

Heretofore hammer mills of this character have I been formed to includeheavy cast metal casings which have been considered necessary in orderto minimize vibration in the operation of the rotor at high speeds andto preserve bearing alignments. In the design of the present mill,however, I use a separate angle construction or subframe composed ofstructural metallic members to which are bolted or otherwise secured thev wall plates. Normally, it would be thought that this constructionwould be ample to avoid defiection but if unprotected such deflectionwould exist. enough in the operation of the mill, even up to 75 H. P.application, to distort this frame structure permanently or reallydamage it in any way,

While almost no force would be great arcades yet there is an initialdeflection before the full resistance of the steel is obtained, whichwould be very detrimental and cause trouble with shafts and bearings.

To overcome this, I use the braces 69 which are connected as shown inFigs. 1 and 2 with the upper and lower sets of angle members 2. In orderto make these braces effective and produce a rigid solid frameconstruction, the lower frame is assembled including the members I, 2,3, l and'i'a, and an expander (not shown) is inserted to spread apartthe upper and lower angles until there is produced a decided buckle inthe side sheets. The braces 59 are then cut to such length that whenthey are inserted and secured, this deflection of the frame will bemaintained following the removal of theexpanding means. In this way, Iovercome entirely any tendency of flexure in the frame. By theemployment of these pressure braces, the middle is relieved entirelyfrom this initial fiexure which would otherwise be present and also I amenabled to avoid the use of inordinately heavy steel members. What isclaimed is: .In a rotary hammer mill, a casing comprising a structuralsteel frame of substantial cubical form, including rigidly united upperand lower sets of horizontally disposed rails and vertically extendingpost rails, sheet metal plates secured to the sides and ends of saidrails and defining a rotor chamber, a rotor arranged in said chamber andincluding a shaft mounted for rotation in bearings carried by' the upperset of horizontally disposed rails, and brace members under compressionuniting the upper and lower sets of horizontally disposed rails andarranged to deflect said frame structure and hold it under tension.

THEODORE C. ALFRED.

